Add a deprecation to old show exceptions API (even though it was not public).

actionpack/lib/action_dispatch/middleware/show_exceptions.rb

@@ -15,6 +15,20 @@ class ShowExceptions
        "application's log file and/or the web server's log file to find out what " <<
        "went wrong.</body></html>"]]
 
+    class << self
+      def rescue_responses
+        ActiveSupport::Deprecation.warn "ActionDispatch::ShowExceptions.rescue_responses is deprecated. " \
+          "Please configure your exceptions using a railtie or in your application config instead."
+        ExceptionWrapper.rescue_responses
+      end
+
+      def rescue_templates
+        ActiveSupport::Deprecation.warn "ActionDispatch::ShowExceptions.rescue_templates is deprecated. " \
+          "Please configure your exceptions using a railtie or in your application config instead."
+        ExceptionWrapper.rescue_templates
+      end
+    end
+
     def initialize(app, consider_all_requests_local = nil)
       ActiveSupport::Deprecation.warn "Passing consider_all_requests_local option to ActionDispatch::ShowExceptions middleware no longer works" unless consider_all_requests_local.nil?
       @app = app